At least Quantium Slipstream is a concept that supports faster than Warp 10 due to the manner in which it is accomplished. We do know what it means to reach Warp 10, and I do prefer when STO stays true to well-established canon. If Borg engines can go Warp 14, then they need to supply a technological reason for this that at least sounds feasible and doesn't break well-established canon.

I know some people don't care if STO breaks canon. However, I do, and so do many others. So yeah, that is out, absent an explanation.

Certainly a readjustment with regard to values would be nice but seeing ST broke it's own canon on numerous occasions then I'd hate to see a canon only game